Fabric attaching cap strip for aircraft



June 13, 1939. c. DE GANAHL FABRIC l^.'I."I.P\CX[NG CAP STRIP FOR AIRCRAFT Filed May 25; 1937 iNvENToR DE/Y/vi/a/L,

ATTORNEY Patented June 13, 1939 PATENT OFFICE FBRIC ATTACHING CAP STRIP FOR A-IR- CRAFT Carl de Ganahl, Bristol, Pa., assignor to Fleet-- wings, Inc., Bristol, Pa., a corporation of Dela- Ware Application May 25, 1937, Serial No. 144,594

8 Claims.

This invention relates to aircraft. In aircraft wings it has been diicult in the past to proportion the strength of the rib structures to the varying stress demands of the Wing v structure. Similarly, in attaching fabric to wings and analogous structures in the prior art, objectionable knots and stitches were '-used that were hard to apply and which enhanced fric- .tional eiects to increase the drag of the craft.

It is among the objects of this invention: to provide a tail rib construction of a tapered closed cap section; to provide means for stitching or securing fabric to a wing without interrupting the smooth external appearance of the fabric; to provide a tail rig construction of varying strength in a simple and economical manner; to provide a tapered cap strip section from stainless steel which can be spot welded into shape with a minimum of expense; and many other objects and advantages as will become more apparent as the description proceeds.

In the accompanying drawing:

Fig. 1 represents a transverse vertical section of a wing according to one form of the invention,

Fig. 2 represents a fragmentary elevation of a portion of the tapered, closed cap section of the invention,

Fig. 3 represents a fragmentary detached perspective of the closed tapered section of Figs. 1 and 2,

Fig. 4 represents a transverse section through the closed cap strip of the invention taken on linev 4 4 of Fig. 1 showing a fragmentary section of fabrics attached thereto, Fig. 5 represents a similar section on line 5-5 of Fig. 1, and

Fig. 6 represents a fragmentary enlarged section of the cap strip to show the construction.

Although obviously capable of use in other connections, and with different types of wings, etc., the invention can be well understood from the aircraft wing disclosure of` Fig. 1. In that illustration a wing Il)l is shown comprising the metal entering edge section Il, terminating at the rear in a vertical spar or shear web I2. l The box like construction of the entering edge portion is of noparticular moment in connection with the instant invention, except to note that it carries the greater part of the load, and has preferably a'metal skin.

Suitably secured to the spar I2 are the tail ribs I3 comprising struts or web members I4 secured to the top and bottom cap strip I5. Preferably, although not necessarily, the struts are constructed in accordance with the disclosure of application Ser. No. 5,191 of Roy A. Miller. The normal load decreases toward the trailing edge I6 so that it is highly desirable to have the rib cap strip sections taper from the connection with the spar I2 toward the trailing edge to decrease the Weight and strength of the parts, as a function of the decrease in the normal load.

Referring to Fig. 3, there is disclosed a cap strip I1 comprising a member having a lower surface or bottom I8, side Walls 20 and 2|, defining an open slot, trough or channel, which merge into the substantially planar integral wings or faces 22 and 23 perpendicular to the respective side Walls, by means of substantially rounded corners I9 and having curled edges 24. Curved corners I9 and edges 24 each are disposed so as to minimize fraying and Wear of subsequently attached fabrics. The cap strip extends substantially full length of the tail rib or as far as desired, and is preferably of the same size throughout. As will be discussed later herein the cap strip may be given a slight curvature to shape the ribs as desired.

At suitably spaced intervals the substantially U or staple-shaped pins 25, comprising the spaced parallel legs 26 and transverse bar 21, are inserted in the trough and spot welded into position. The transverse pins are reinforcements for the cap strip assembly, and as will later be discussed, form rigid stitching points for the attachment of a fabric cover for the ribs.

The entire cap strip assembly is comprised of the cap strip I1, either with or without the transverse pins or staples 25, with the U-shaped tapering depth member or channel section 30. This is of the simplest of formations, comprising an initially fiat strip of metal having non-parallel and convergent side edges 3| and 32, which may if desired b'e non-linear so as to facilitate the imparting of a suitable curvature to the capv strip. The edges are brought toward each other symmetrically by bends about the center 36 of the strip to form a channel member having spaced4 substantially parallel legs 33 and arranged to straddle and engage the outer surfaces of walls 20 and 2| of the capstrip, until the edges' 3| and 32 substantially abut the under surfaces of the cap strip wings 22 and 23. If edges 3| and 32 are given a slight curvature, it will be understood that abutment thereof against wings 22 and 23 will require a curvature of the cap strip which i may be permanently setlf the channelv and cap strip are anchored together in this position. The depth member is easily spot welded or riveted in place by the welds, or the like, 35, as by bringing the welding contact electrodes against the outer surfaces, while holding a removable copper electrode of the same thickness as the slot in the welding, with rolling electrodes or the like, or

\ at least in the preferred construction, so that when bent about the center of the strip, the column is therefore tapering in its longitudinal extent, as will be obvious.

Thus, as shown in Fig. 4, the entire cap strip v "column orv section will be of considerable depth because of the space between the bottom wall I8 of the cap strip and the curved rear wall portion 36 of the depth member, whilethe section shown in Fig. 5 is of decreased weight, depth andstrength suitable flexible stitches or metallic clips 40 ap as the curved wall 36 integral with that of Fig..4, is closer to bottom surfaces I8 of the cap strip. Thus in a simple and highly economical construction a tapering cap section is provided for the tail ribs, which. is capable of easy association with the closed section or other struts I4, in any desired manner.

- The tail ribs including the cap strip sections described, with the open troughs or slots presenting outwardly, form an excellent bearing and attaching" framework for fabric skins or wing covers. The fabric, such as linen or the like, in a continuous sheet 31 extending over several ribs, is, for safety, provided preferably with an internal tape of fabric 38 aligned with individual ribs,lof such width as to extend laterally beyond the curled edges 24 of the cap strip wings, and of such length as to cover the entire cap strip. The tapes may be stitched to the wing fabric, or secured by dope, or in any other desired manner. The fabric and attached tape, if used, is then stretched over the ribs, upon which it is supported by the flat areas of wings 22 and 23 of the cap strips, between the curved non-chafing edges I3 and 24 thereof, and'in certain cases upon the transverse reinforcing members 25 as well, depending upon the dispositions thereof. Usually and preferably the transverse reinforcements 25 have the upper surface of bar 21 just below the level of the planar wings 22 and 23, in order to minimize contact of the fabric therewith, as if it is slightly higher, it tends to indent the fabric with the cross bars. This is usually undesirable, although it will be governed by necessities as to supporting areas.

With the fabric'and tape, if used, on the ribs,

plied by any suitable stitching or stapling mechanism or by manual means (not shown), are passed through the fabric, and tape, and about cross bars 21 of the reinforcements 25. The stitches are suitably tied, secured or knotted on top ,of the fabric. This stitching at each, or at selected cross bars, securely ties the fabric to the cap strips, in an efficient, and economical manner, without the creation of raised knots, and the like, and is facilitated by the clearance afforded below the cross bars 21 by the depth of slot 9 of the cap strip.

If desired a second tape 4| may be stretched over the fabric and the stitching to cover same to finish the surface and free it from the frictional effects of the small knots of stitches 40. This is not usually necessary however, as the structure shown causes the fabric and knots to be slightly indented instead of protuberant as might occur if the cross bar 21 was exactly in the plane of wings 22 and 23, instead of slightly out of this plane as shown. Tape or strip 4| may be doped into position, or otherwise secured.

I claim:

1. A cap strip section for aircraft ribs, comprising an integral channel member comprised of a bottom wall, spaced side walls, wings extending laterally of the side walls to form bearing surfaces for fabric, the wings having a curved longitudinal bead on the free edge to minimize fabric chai-lng, the space between the wings comprising an elongated slot or trough and a plurality of thin straight anchoring and reinforcing elements disposed close to the average plane of the wings and rigidly secured within the trough substantially perpendicular to the side walls of the channel members.

2. A cap strip comprising an integral channel member comprised of a bottom wall, separated wings spaced from the bottom wall, spaced side walls joining the wings and bottom wall, and a plurality of transverse reinforcements extending between and rigidly attached to the side wallsK each comprising asubstantially cylindrical member perpendicular to the side walls close to the 3 plane of the wings.

3. A cap stripcomprising a bottom wall and integral side walls of uniform depth, and a substantially U-shaped tapering channel member having walls straddling and engaging the side walls, and means connecting the side walls and channel walls together to form a tapering cap strip section, and narrow spaced reinforcement and fabric anchoring members rigidly fastened to and extending transversely between said side walls.

4. A cap. strip section for aircraft ribs, com-v laterally of the side walls and having a,y trough a between the side walls, a substantially U-shaped channel member having spaced walls straddling and engaging the respective side walls and substantially abutting said wings, and a plurality olf spaced laterally extendingreinforcements rigidly attached and engaging and extending between the side walls in the trough.,

6. A cap strip for ribs comprising a channel member having an open side and a closed bottom, side walls rising in spaced relation from the closed bottom, wings extending laterally from the side walls in a substantially common plane, reinforcing anchoring devices comprising substantially U-shaped, pins having legs rigidly engaging the respective side walls and a cross bar extending rigidly between the side walls close to the plane of said wings, and means securing the legs to the respective side walls. v

7. A cap strip section for ribs comprising an angular channel section composed of a bottom Wall, substantially parallel side walls at each side of the bottom wall, and substantially planar wings extending laterally of the side walls,1a section comprised of a substantially U-shaped channel having legs arranged to overlie and engage throughout their depth the said side Walls, said legs substantially abutting the inner sides of said wings, said legs and side wallsbeing welded together, and reinforcements rigidly attached to and extending laterally between the side walls substantially close to the plane of the wings to anchor fabric thereto.

8. A capstrip section for ribs comprising an angular channel section composed of a bottom wall, substantially parallel side walls at each side of the bottom wall, and substantially planar Wings extending laterally of the side walls, a section comprised of a substantially U-shaped channel having legs arranged to overlie and engage throughout their depth the said side walls, said legs substantially abutting the inner sides of said wings, said legs and side walls being welded together, and reinforcements extending laterally between the side Walls, and including legs engaging and welded to inner surfaces of said side walls.

CARL ns GANAHL. 

